This Phase I, open-label, dose escalation clinical study of the immunotoxin RFT5 -SMPT-dgA (IMTOX 25) in patients with CD25+ non-Hodgkin's lymphoma or leukemia is being undertaken in order to determine the max tolerated dose, assess the safety, including dose limiting toxicities, analyze pharmacokinetics and in vivo stability of IMTOX 25, determine antibody responses to the two components of the immunotoxin, and document clinical response and biologic effect.